These actuators are often contained in a cylindrical enclosure when they control the movement of roller blinds and in a parallelepipedal enclosure when they control the movement of venetian blinds.
Apart from very specific applications requiring an independent accumulator battery and/or solar panel type power supply, these actuators are powered from the low voltage (LV) AC mains supply (electric power grid, 110 to 230 V, 50 or 60 Hz, depending on countries) and the electric motors used in these actuators are normally of single-phase asynchronous type (induction motor) with permanent capacitor.
However, it is proving advantageous to replace such alternating current motors with permanent magnet DC motors, designed to operate at an extra low voltage (ELV), that is, more often than not, less than 48 V. Such motors are produced in very large quantities, in particular for automobile applications, and their cost is therefore low.
Furthermore, the DC motor is well known to offer wide flexibility of use. In practice, the rotation speed can be controlled by the rotor power supply voltage and obstacles can be detected by analyzing the rotor current which reflects the motor torque.
However, converting a low voltage AC electrical source into an extra low voltage DC source raises problems. Indeed, the dimensions of the components required lead to a physical separation between the power supply converter and the actuator. This separation is not practical: it means having to arrange a second location to accommodate the power supply module and, above all, having to provide a large section cable connecting line to power the DC motor. This connecting line also presents the drawback of radiating interference generated by the electrical switching action of the motor commutator.
Patent FR 2 692 418 discloses a solution to this type of problem. It proposes, like other documents of the state of the art, that each venetian blind casing should simultaneously house the extra low voltage DC motor, a battery and a converter device formed by a transformer and a rectifier (FIG. 3 of this patent). The battery is used to store energy. Because of this, the converter device is simply dimensioned for slow recharging of the battery, which means that its dimensions can be reduced. There is nothing in this embodiment to suggest grouping all of these elements in the actuator: they are clearly represented physically separate within the casing. However, for issues of battery life and maintenance, it makes sense to allow for its easy replacement.
Such a solution presents an obvious drawback: it limits the number of operations to the battery capacity, which can be recharged only slowly.
Patent application EP 0 852 281 discloses a tubular actuator comprising a reduction gear, a DC motor and an electronic control board also serving as mains powered power supply. It states that this board can in effect be used to replace the transformer, the size of which is incompatible with installation in the tube. The solution recommended in this document consists in replacing such elements with a power electronic unit comprising a coil mounted on a ferrite core, a diode, a rectifier bridge and a capacitor.
It also states that the remote control of the actuator can be achieved by known means such as an infra-red link or a radio-wave link.
The problem raised by this arrangement lies in the miniaturization constraints evoked in the prior art, but also in the cohabitation relationships between the various elements. In practice, the latter dissipate and receive thermal energy, although their own performance characteristics are affected by temperature, send and receive electromagnetic interference, although the performance of one of them is directly affected by the electromagnetic field and, finally, send and receive conducted interference on their power supply line.
Patent application EP 1 091 078 discloses a motorized blind device in which the motor is of low voltage type and is powered from the mains supply via a low voltage AC/DC converter. The use of a low voltage motor raises certain problems. In practice, these motors are difficult to produce and are expensive. In the proposed embodiment, the operation of the converter runs the risk of disturbing the command receiver located nearby.
Also, in a quite different field, patent U.S. Pat. No. 5,818,703 discloses a voltage step-up DC/DC converter intended to power a cardiac defibrillator, the switch of which operates at high frequency.
The object of the invention is to improve the actuators of the prior art and resolve the abovementioned problems. In particular, the invention proposes to combine within a given space, a DC motor, a motor power supply control board and a voltage converter, the control board comprising a radio-wave receiver. The operation of such an actuator must also be reliable.